Cornea cannot receive oxygen from the blood supply like other tissue. When the eye is open, the cornea primarily receives oxygen from the atmosphere, via the tears.
When the eye is closed (e.g., during sleep), the cornea receives oxygen mainly from oxygen diffusion from the capillary plexus of the upper palpebral aperture vasculature. If sufficient oxygen does not reach the cornea, corneal swelling occurs. Extended periods of oxygen deprivation cause the undesirable growth of blood vessels in the cornea. Wearing of a soft contact lens inevitably reduces the oxygen supply to the cornea, because it can form an oxygen barrier that prevents oxygen from reaching the cornea. The oxygen transmissibility (Dk/t) of the contact lens worn by a patient, depending upon the oxygen permeability (Dk) of the lens material and the thickness (t) of the contact lens, is of vital importance for the oxygen supply to the cornea either from the atmosphere in the open eye state or from the capillary plexus of the upper palpebral aperture vasculature.
In recent years, soft silicone hydrogel contact lenses become more and more popular because of their high oxygen transmissibility and comfort. Silicone hydrogel (SiHy) contact lenses are made of a hydrated, crosslinked polymeric material that contains silicone and from about 23% to about 75% by weight of water within the lens polymer matrix at equilibrium. Exemplary commercial SiHy lens products are Focus® Night & Day® from Alcon Corporation (ca. 23.5% H2O and Dk˜140 Barrers; Air Optix® from Alcon (ca. 33% H2O and Dk˜110 Barrers); DAILIES TOTAL1® from Alcon (ca. 33% H2O in bulk, >80% H2O in surface, and Dk˜110 Barrers); PureVision® from Bausch & Lomb (ca. 36% H2O and Dk˜140 Barrers); Ultra from Bausch & Lomb (ca. 46% H2O and Dk˜114 Barrers); Acuvue® Oasys® from Johnson & Johnson (ca. 38% H2O, Dk˜105 Barrers); Acuvue® Advance® from Johnson & Johnson (ca. 47% H2O, Dk˜65 Barrers); Acuvue® TryEye™ from Johnson & Johnson (ca. 46% H2O, Dk˜100 Barrers); Biofinity® from CooperVision (ca. 48% H2O, Dk˜128 Barrers); Avaira™ from CooperVision (ca. 46% H2O, Dk˜100 Barrers); MyDay™ from CooperVision (ca. 54% H2O, Dk˜80 Barrers); and PremiO™ from Menicon (ca. 40% H2O, Dk˜129 Barrers); Clariti® from CooperVision (ca. 56% H2O, Dk˜60 Barrers); Definitive™ from Contamac, Ltd (ca. 75% H2O, Dk˜61 Barrers). However, a SiHy contact lens may not have a very high oxygen permeability (e.g., greater than 180 Barrers). A very high oxygen permeability is likely required for alleviating the adverse effect of oxygen-impermeable electro-optic elements, which are incorporated in contact lenses (see, U.S. Pat. Nos. 6,851,805, 7,490,936 and 8,154,804), upon the permeation of oxygen through the contact lenses.
Silicone contact lenses, made essentially of a crosslinked silicone polymer (or a silicone rubber or elastomer), have been proposed previously (U.S. Pat. Nos. 3,916,033; 3,996,187, 3,996,189; 4,332,922; and 4,632,844, herein incorporated by references in their entireties), because of their very high oxygen permeability and good mechanical and optical properties. However, because a silicone polymer is a hydrophobic material, a silicone contact lens has a hydrophobic surface and thereby is not ophthalmically with the cornea. It may irritate the corneal tissue and cause adverse event.
Recently, Matsuzawa discloses a plasma polymerization method for applying an amorphous carbon film onto the surface of a silicone contact lens (U.S. Pat. No. 9,010,933, herein incorporated by reference in its entirety). Resultant silicone contact lenses can have a very high oxygen permeability and good wettability as measured by a water contact angle (herein designated as “WCA”) of about 25 degrees. However, such plasma polymerization method may not provide a silicone contact lens with a desirable surface hydrophilicity (as measured by water-breakup-time, hereinafter designated as “WBUT”) and lubricity. Further, Matsuzawa has not reported whether such silicone contact lenses with an amorphous carbon film could maintain their wettability when being exposed to air or stored in a dry state for a prolong period of time. It is known that silicone has a great tendency to migrate to the surface of a substrate in the air to minimize the surface energy.
Therefore, there is still a need for an improved method for producing silicone contact lenses with a thermodynamically-stable, lubricious coating. There is also a need for silicone contact lenses with such a thermodynamically-stable, lubricious coating thereon.